The objective of this research is to broaden our knowledge on the protective function of the skin. More specifically to study the structure, formation, fate, and chemical nature of the poorly characterized "membrane bound granules" in the epidermis. To achieve this goal, correlated electron microscopic, autoradiographic and histochemical studies, as well as isolation and chemical characterization of the granules is planned. The skin of several vertebrates living under different environmental conditions will be employed.